Disk-shaped data storage media, such as magnetic diskettes and certain types of optical storage discs, e.g., magneto-optic disks, are typically protected by enclosures, or cartridges, which reduce contamination to the disk due to dust and debris. Such enclosures typically provide apertures covered by sliding shutters to allow access to the media by a disk drive.
As shown in FIG. 1, a disk-shaped storage medium 40 is usually protected by an upper cartridge shell 12 and a lower cartridge shell 14 which fit together to form a complete cartridge 10. A drive may gain access to media 40 by sliding shutter 16 on cartridge 10 to an open position. Partitions are provided within the cartridge 10 to subdivide the enclosed space into various compartments. The partitions are typically formed by ribs which are provided on the interior surfaces of shells 12 and 14. Typically, each rib has a height equal to about half of the distance between the interior surfaces of shells 12 and 14 when the cartridge 10 is assembled. The ribs are aligned so that they mate with each other to form compartments within cartridge 10. Ribs 20 and 22 form a compartment 30 that separates medium 40 from compartments 18.
As shown in FIGS. 1 and 2, a compartment 30 is a circular space bounded by interior surface 15 of lower cartridge shell 14 and the interior surface of upper cartridge shell 12, and is within the circular boundary defined by ribs 20 and 22. Compartment 30 may further include a rib 24 on interior surface 15 of lower cartridge shell 14 which defines a circular boundary concentric with rib 22 for supporting medium 40 in an outer circumferential area 42 of the medium which is not intended to store data. Compartment 30 may also include yet another rib 26 on interior surface 15 of lower cartridge shell 14 which defines a circular boundary concentric with rib 22 for supporting medium 40 in an inner circumferential area 46 of the medium which is not intended to store data.
Rib 22 defines the circumferential boundary of the lower portion of compartment 30. The radius of the boundary is slightly greater than that of medium 40.
A cross-sectional view of ribs 20 and 22, taken along line 3-3' in FIG. 1, is shown as FIG. 3. Rib 22 extends upward from interior surface 15 of lower cartridge shell 14 and rib 20 extends downward from interior surface 13 of upper cartridge shell 12 to form a smooth continuous wall when the upper and lower cartridge shells are assembled as cartridge 10. Ribs 20 and 22 may be of a precisely determined height that allows them to contact at their tops at interface 38, thereby forming continuous rib wall separating compartment 30 housing media 40 from compartments 18. In the alternative, a small gap may be provided at interface 38, as shown in FIG. 3.
Rib walls which contact each other at their tops suffer, however, from the disadvantage of requiring very tight manufacturing tolerances, since the rib edge surfaces forming interface 38 must be in close proximity to each other, yet must have very limited interference to avoid causing a deformation of upper and lower cartridge shells 12 and 14 at locations 50 and 52, respectively, which might result in unsightly bulges or cause cartridge 10 to malfunction. Alternatively, if a gap is provided between the two rib tops, debris particles may be able to migrate through the gap and onto medium 40.
Drives for reading and/or writing data on disk-shaped optical storage media have error detection and correction codes (EDCC) incorporated in the drives' system electronics and firmware which allows for a potential loss of data bits by decoding them within the context of the retrievable data. However, should too many consecutive bits of data be lost due to a large debris particle or an accumulation of smaller debris particles, the EDCC system would be unable to decode the lost data. As new media products having increased storage density per unit area of media are developed, the newer media is increasingly sensitive to debris accumulation and smaller debris particles because of the closer spacing of the data bits.
An alternative prior art rib configuration is shown in cross-section in FIG. 4. Rib 20' has a notch on one side of its top, causing the rib to be higher on one side than the other. Rib 22' is notched in a complementary fashion, so that the extended portion 62 of rib 20' mates with the shorter portion of rib 22', and the extended portion 64 of rib 22' mates with the shorter portion of rib 20'. This overlapping design is less sensitive to manufacturing tolerances and thus allows for a relatively wide dimensional variation without causing noticeable deformation of the cartridge at locations 50 and 52. This configuration also provides a gap that is more convoluted, thereby making it more difficult for debris particles to pass through the gap.
If cartridge 10 is to be formed by the injection molding of a thermoplastic material, it is desirable that ribs 20' and 22' be relatively thin, since ribs that are thicker than the wall from which they extend can cause defects, called sink marks, at locations 50 and 52 of the cartridge. However, due to the configuration shown in FIG. 4, ribs 20 and 22 must be even thinner at their top portions 62 and 64, respectively. This makes the ribs difficult to fill during molding.
A second alternative prior art rib configuration is shown in FIG. 5. Ribs 20' and 22" resemble ribs 20' and 22' of FIG. 4, but differ in that they have a more gradual transition between the shorter and longer portions, 62' and 64', respectively, of the ribs. This design suffers from some of the same disadvantages as the rib configuration of FIG. 4.